If she is the incarnation of Qetesh it would make sense she's need a surrogate just like Nergal, though maybe as a "ghost" she can possess someone.
I think she's not the incarnation of quetesh, but Quetesh herself, and unlike Nergal she has worshipers and enough power to manifest directly
Gods cannot manifest for long times on the mortal plane. Tinkerer told me it's kinda like Warhammer rules, the more powerful the Supernatural entity (demon, angel ect...) the harder it is for them to maintain a presence cos there isnt enough magic to maintain them. Eventually even Lesser Demons & Demon Hounds would become unstable, popping back to their reality. As Deities I think it may be too much to try to enter our world. They probably would only be able to physically be there for like a few seconds before they are forced back. If this "Ghost" is Qetesh it's most likley an ethereal apparation being sent to visit MC but Qetesh herself is still physically in her own domain (probably still takes a bit of energy just to manifest that tho).
Would be cool if she shows MC a way to come to her. Imagine using a special portal gate to travel to Qetesh's domain to visit her. MC has proven it's possible to cross into the Realm of the gods so why not? I imagine her domain to be a lush overgrown garden littered with temple structures & statues (naked statues, dicks, tits, people having sex). With like Cherubs or other types of angel servants flying around. Also if MC gets her preg the children could just live there with her (heck mabey she births said Cherubs?).
Currently Nergal has the stronger following, hence why he was able to directly talk to Erevi & shock her through his statue. I would expect that he has a strong following among the Dark Elves & some more wicked human cults. Qetesh has spent the last 20 years being starved of worship & sacrifice which is why she has had so little interaction with the Temple. She has manifest her pleasure in response to mass & now she can manifest a, silent, apparition to wander the Temple for short times. Next update I think is the turning point as she can now manifest a detailed apparition. Give her some time & more worshippers, she may be able to actually speak to MC/the Qeteshians.
there's a chance that nergal being the god of death, destruction etc is barren and couldn;t knock quetesh up.
Nergal is Lord of The Underworld, not death. There is already a different Lord of Death in this game. Nergal is more like Satan I think so I dont think he would be infertile. Mabey Qetesh being a goddess of fertility can choose who can knock her up?